Food safety in antiquity : how and why Early Roman Period Jerba had no problemto sustain itself

Antoine Bourrouilh

Paris, France, October 2015

# Introducing the core problem : can the question of Early Roman Jerba importingcereals so easily answered?

Having both a strong interest in numerical approaches in archaeology and in the Roman period, I could not have been more delighted than discovering that my preferred library just received "Quantifying the Roman Economy - Methods and Problems" [Bowman, Wilson 2009].

In this book Elizabeth Fentress wrote a paper about demography and the countryside [Fentress 2009]. She gives some estimations of both the rural and the urban populations of the island of Jerba (Tunisia) in Roman times based mainly on land surveys. Once stated, these minimum and maximum numbers are used for subsequent reflections. First of them, food estimations [Fentress 2009: 139-140].

Before making any computations, the author states that her calculated urban ratio population of 42% means that grain must have been "imported in considerable quantities". She points to a 1981 book on demography in archaeologyto sustain it [Hassan 1981]. This latter work is not in question here, at least not directly. However, the subsequent calculations to go beyond this hypothesis and assert that Jerba WAS a grain importer are.

# The background calculations

Food estimations based upon assumptions on agriculture technology are rather straight forward. These calculations are used for decades by archaeologists to make site catchment analysis. E. Fentress used an estimation of 1,550 metric tons of wheat produced on the whole island (1,550,000 kg). As she states, only afew thousands people can live on this, well below her 'best guess' estimation of31,000 inhabitants. Jerba surface is given at just over 500 km² (514 km² with today shores, but surprisingly in the article it is said to be just under 600 km²). Nevertheless, a production of 1,550,000 kg of wheat seems fairly low for this scale of surface, even if E. Fentress underwrote that this estimation involved only the "richest soils" of the island. So, we are going to check the calculations in depth, which implies browsing the bibliographical references.

# Along the bibliographical path

As a matter of fact, she has not computed this estimation herself, at least not directly. Indeed, she points to the work of M. Frachetti who handles the geographical part of one of her own collective book on Jerba [Frachetti in

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Fentress et al. 2009: 55-70]. Thus, it seems that the historian job of estimating Roman Jerba cereal productivity was made by a specialist in Geographical Information System (GIS) [Fentress et al. 2009: 12].

In the aforementioned book, the reasoning behind the calculus which leads to the1,550,000 kg assumption is present, although in a short footnote. It is based upon:. an estimation of the need of cereals per year, per individual. a map of the soil of Jerba which leads to an estimation of the surface dedicated to cereals. an estimation of the average grain yield based upon a book of R. Sallares fromthe early 90's, "The ecology of the ancient Greek world" [Sallares 1991: 380]

We are going to tackle each of these points.

# The need of cereals per year, per individual

The number used by M. Frachetti is 200 kg of grains per year per individual. This value is consistent with the one we could use [Comet 1992: 311].

# The soil map.

The first point here is that we do not know exactly where this map comes from. Yet, there is the three capital letters "MDP" at the lower right corner [Frachetti in Fentress et al. 2009: 63]. Their exact meaning does not seem to bepresent in the book. They must have been a kind of signature of M. Frachetti, asE. Fentress wrote that he was the one in charge for the maps [Fentress et al. 2009: 12]. So we cannot assert that this map originates from a professional pedological study. However, an official soil map drawn by two paedologists from the French O.R.S.T.O.M is easily available [Pontanier, Vieillefon 1977] (figures1 and 2). As we cannot rely on the one in [Fentress et al. 2009] because of the lack of references, we will use the one from the O.R.S.T.O.M. as our main sourcefor the rest of this work.

M. Frachetti used his map to restrict the surface dedicated to cereal productionto a "conservative value" : only 205 km² (20,500 ha). Indeed, this is close to just one third of the island. It is argued the surface is trimmed down to match "the best 20,500 ha of soil on the island" [Frachetti in Fentress et al. 2009: 62]. Interestingly, in the following paragraph, M. Frachetti wrote that one can add 22,000 ha of "limited potential" soils to this surface. M. Frachetti describes the whole extent as "the total arable territory". If we do the math, this is 42,500 ha or 425 km². However, very surprisingly, he did not use this value to make his final computation of cereal production, besides concluding that the calculated cereal production of 1,550,000 kg involves "all the arable land" [Frachetti in Fentress et al. 2009: 64].

As a matter of fact, the professionally drawn pedological map from the O.R.S.T.O.M. gives us the scale and extent of lands according to their quality regarding agriculture (figure 1 and the close-up on Jerba, figure 2). We can figure out that nearly the whole surface of Jerba is ok for cereal production : only the part in green and blue are said to be "non cultivable" by the two paedologists, mainly coastal areas and a couple of linear outcrops inland.

So, we have to consider that, except some areas on the coast line and inland, nearly the whole island is suitable for cereal production. This is our main

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starting hypothesis for Roman Jerba. This assumption can be partly supported by some sub-contemporary written sources about Jerba. Thus in the "Monographie de l'Ile de Djerba" by A. Brulard written in 1885, we can read on page 19 : "le solde l'île, partout sec et sablonneux, sauf sur la côte ouest , où il est caillouteux, n'en est pas moins d'une très grande fécondité" [Brulard 1885: 19],which can translate into : "the soil of the island, everywhere dry and sandy, except on the west shore where it is stony, is nevertheless fruitful". A. Brulard adds : "nous avons vu peu de territoires aussi fertiles dans toute la Tunisie" [Brulard 1885: 20], which translates into "we saw few such fertile territories in whole Tunisia".

The whole point about this soil map discussion is to assess the capacity of the island regarding agriculture, especially cereal production. As we just saw, nearly the whole island has to be taken into account for Roman Jerba. Considering (i) the O.R.S.T.O.M map and (ii) the fact that a part of antique Jerba is under water [Brulard 1885: 6], we can estimate that between 400 km² and500 km² from the present 514 km² of Jerba surface can be considered as suitable for cultivation. We will settle on the mean: 450 km². We can note that this value is very close to the 425 km² "total arable territory" estimation, that M. Frachetti should have used (see above). This 450 km² hypothetical extent has to address the basic need of feeding the island population. Regarding food safety, one cannot trim down this number to a lower number on grounds not historically supported by strong arguments.

On this very point, one cannot also discriminate between different arable land qualities ("the best 20,500 ha" of M. Frachetti) based on our present criteria, without also discussing it historically. Moreover, an historian perspective leads also to more interesting and challenging reflections, far from just writing off 22,000 ha of arable land from Roman Jerba. For instance, consideringlate 19th century and sub-contemporary Tunisia, one can learn from the work of J. Hassainya that, if two kinds of arable land can be discriminated, it matches land property divisions between the bigger colonial exploitations and the small traditional households [Hassainya 1991: 40]. But, above all, it also means that these best lands did not feed local people : besides producing mainly cereals, these colonial exploitations (and a couple of rich Tunisian landowners) exportedthe greater part, mainly to continental France. We may be far from the Roman Antiquity (or are we as J. Hassainya suggests?), but in any case, this example was only here to show how far from reality a conclusion can be in social historywhen only supported by environmental grounds.

# The average grain yield

The average grain yield used by M. Frachetti is 150 kg/ha for Roman Jerba. Firstly, one has to point out that the cereal variety is not mentioned along this number. Secondly, it has to be said that, whatever the cereal, this number is really very very low. To give some clues, for 18th century France and common wheat, a very good soil is assumed to give 2400 kg/ha whereas the poorest soil only 690 kg/ha [Comet 1992: 299]. If we consider : (i) 20th century Tunisia,(ii) native exploitations, i.e. non-colonial, (iii) government official statistics, (iv) between 1928-1949, G. Comet – quoting [Pissaloux 1955] – relates that the mean yield for common wheat was 540 kg/ha and for durum wheat 340 kg/ha [Comet 1992: 309]. He adds that according to R. Pissaloux these numbers should be revised upwards. Indeed people tend to underestimate their productions, fearing taxes and mistrusting the government.

A minimum yield

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These numbers are for whole Tunisia. However we can focus on an area closer to Jerba. Indeed A. Abaab , A. Tbib and M. Ben Salem wrote a paper on family agriculture in the Médenine and Tataouine sectors. In this continental arid area, the mean yields for cereals cultivated with dry-farming and only-plowing methods (non-irrigated techniques) are between 300 and 400 kg/ha for barley and 200 and 300 kg/ha for durum wheat [Abaab, Tbib, Ben Salem 1991: 156]. Jerba belongs to the Médenine "gouvernorat". However, being northernmost and as an island, the climate in Jerba is better regarding agriculture. Thus we have to consider that 400 kg/ha can be taken as the very low floor for durum wheat yieldcultivated on the island with non-irrigated techniques.

An interval

This leads us to an interesting point. The cereal yield in arid or semi-arid areas depends firstly on the water availability. Mainly this water can come directly from precipitations or irrigation. Thus, in Ksar Ghilane – roughly one hundred kilometres west of Tataouine – an area far worse than Jerba regarding agriculture, yields on irrigated experimental fields were between 500 and 800 kg/ha for durum wheat and between 900 kg/ha and 1300 kg/ha for barley [Cointepas1960]. The point here is that Tunisia has a long history with irrigation, starting well before Roman Empire Period, and obviously used during this era as well [Hassainya 1991: 22-24]. Thus, if we consider Roman Jerba, a ceiling yield of roughly 1000 kg/ha for durum wheat is a likely value. So the min-max range for durum wheat yields on Roman Jerba spreads from 400 kg/ha to 1000 kg/ha. These values must be taken as a theoretical confidence interval where the mean yield must be. If we consider barley, these values are higher : 500 kg/ha and 1500 kg/ha as a mininum and maximum.

Where the devil hides ...

One can wonder now why M. Frachetti retains such a non-realistic value of 150 kg/ha from R. Sallares book? Indeed, as a matter of fact, R. Sallares himself considers 500 to 800 kg/ha as being "extremely low yields" [Sallares 1992: 372].The 150 kg/ha yield reference is located on page 380 : R. Sallares states that this is the yield "of the durum wheat cultivated by indigenous farmers in the arid central and southern regions of Tunisia" after WWI. The point here is that (i) R. Sallares did not give a single reference to justify this number, (ii) thearea mentioned, except for being in Tunisia, as little if nothing to do with thesemiarid Mediterranean climate of Jerba. Those are two reasons not to consider this yield as a direct proper value for Roman Jerba. However, that being said, this value was chosen. The reason lies in the sentence directly following the 150 kg/ha reference. R. Sallares wrote, still on page 380 : "There is no reason whatsoever for supposing that it was any higher in antiquity". That is where thedevil lies, because this sentence can be easily misunderstood. The first meaning, which is the right one, is that in "arid central and southern regions of Tunisia", the yield was likely not higher in antiquity than just after WWI. The second meaning is that yields could not have been higher in the whole antique world. It is obvious that this second meaning cannot be the right one. However, sadly, in all likelihood this is the one retains by M. Frachetti. In fairness to him, it has to be said that this chapter of R. Sallares book about cereal yields is very very confusing : in the few couple of pages preceding the 150 kg/ha paragraph, R. Sallares mentions (i) the theory of the deterministic chaos (p. 375), (ii) Darwin and his theory of The Origin of Species (p. 376) (iii) Michel Foucault and his concept of "system of thought" (p. 380). However, at the very basis, R. Sallares book should not have been chosen as a proper source to document Roman Jerba yields. As already said, R. Sallares yield value cannot be applied directly to Jerba and is not sustained by any reference. Moreover, as we have seen, sources to discuss proper cereal yield values interval for Roman Jerba are available.

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# Conclusion

With proper cereal yields and cultivation areas, we can go back to our main question : what level of population would Roman Jerba could have sustained and how it compared to E. Fentress calculations? Considering durum wheat, the min-max interval is 400 kg/ha to 1000 kg/ha. As we have seen, 450 km² (45,000 ha) can be devoted to cereal cultivation. We have to divide this surface by two to account for fallow fields. Thus the total annual production ranges from 9,000,000 kg to 22,500,000 kg of cereals, considering durum wheat. That is higher by a factor from 6 to 15 compared with the estimation calculated in [Frachetti in Fentress et al. 2009] and used in [Fentress 2009] (see above).

This scale of production implies a theoretical supported population ranging from45,000 to 112,500 inhabitants (200 kg/year/inhabitant). E. Fentress calculationsled to a minimum of 17,840 inhabitants and a maximum of 44,540 [Fentress 2009: 137]. Her "best guess" was 31,000 [Fentress 2009: 138]. We understand that by noway this level of population could have been a problem for Jerba resources regarding cereal production. Indeed, in the worst case scenario, the maximum number of inhabitants does not reach the minimum of our theoretical interval: 44,540 versus 45,000.

As a final word, we can only regret that food safety of Roman Jerba did not drawthe needed attention in [Fentress et al. 2009]. As a starting point, our own reflection lets us believe that if at some point during Roman Antiquity, Jerba did really import its cereals on a regular basis, it was not directly driven by population pressure, but by choices in the production system, which itself had to fit into the wider imperial trade system.

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# Bibliography

Abaab, A., Tbib A., Ben Salem M., (1991). "Agriculture familiale et revenus extérieurs dans le Sud-Est tunisien". In : Bourenane N. (ed.), Campagne P. (ed.). Pluriactivité et revenus extérieurs dans l'agriculture méditerranéenne. Montpellier : CIHEAM. p. 147-168 (Options Méditerranéennes : Série B. Etudes et Recherches; n. 5)

Bowman, A. K., & Wilson, A. (2009). Quantifying the Roman economy: Methods and problems. Oxford: Oxford University Press.

Brulard A. (1885). Monographie de l'Île de Djerba, Besançon, Typ. & Lith. Ch. Delagrange , 1885.

Cointepas, J.-P. (1960), Compte rendu concernant la parcelle d'essais de Ksar Rhilane, Période 1952-1960, (E-S 30) République tunisienne, Secrétariat d'état àl'agriculture, H.A.R., Section Speciale d'Études de Pédologie et d'Hydrologie.

Comet, G. (1992). Le Paysan et son outil. Essai d'histoire technique des céréales (France, VIIIe - XVe siècle), Rome : École Française de Rome, 756 p. (Publications de l'École française de Rome, 165)

Fentress, E. (2009). "Peopling the countryside: Roman demography in the Albegna Valley and Jerba". In : Bowman A. (ed.), Wilson A. (ed.), Quantifying the Roman economy : methods and problems. Oxford University Press.

Fentress, E. et al. (2009). An island through time: Jerba studies. Portsmouth, RI: Journal of Roman Archaeology.

Hassainya, J. (1991), "Irrigation et développement agricole : l'expérience tunisienne". In : Hassainya J. (ed.). Irrigation et développement agricole : l'expérience tunisienne. Montpellier : CIHEAM. p. 1-217 (Options Méditerranéennes : Série B. Etudes et Recherches; n. 3).

Hassan, F. A. (1981). Demographic archaeology. New York: Academic Press.

Pissaloux R. (1955). Production agricole et alimentation humaine en Tunisie, Cahiers de Tunisie, n° 12, 3e année, 4e trimestre 1955.

Pontanier R., Vieillefon, J., (1977). Carte des ressources en sols de la Tunisie, Feuille spéciale : Gabès-Sidi Chammakh, Échelle : 1/200 000, par R. Pontanier et J. Vieillefon. (Pédologue O.R.S.T.O.M.), Tunis (TUN) : Ministère del'agriculture, DRES. Direction des ressources en eau et en sols ; Paris (FRA) : ORSTOM, Office de la recherche scientifique et technique outre mer, Mission en Tunisie, 1977. - 1:200000. - 1 carte en coul. dépl. h.t. ; 55 x 66 cmhttp://sphaera.cartographie.ird.fr/carte.php?num=2892http://sphaera.cartographie.ird.fr/images/telechargement/02892.pdf

Sallares, R. (1991). The ecology of the ancient Greek world. Ithaca, NY: CornellUniversity Press.

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# Figures

figure 1 - pedological map of Tunisia, special sheet of Gabès-Sidi Chammakh [Pontanier, Vieillefon 1977].

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figure 2 – close-up on the island of Jerba from the pedological map of Tunisia, special sheet of Gabès-Sidi Chammakh [Pontanier, Vieillefon 1977].

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